1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, as wiring of the semiconductor device, Cu is being used instead of Al in order to reduce wiring resistance and to improve the resistance to migration such as electromigration (EM) and stress migration (SM) which cause defective wiring.
Because Cu is hardly fabricated by RIE (reactive ion etching) unlike Al, wiring of Cu is formed with a damascene method by which a recessed portion composed of trenches and holes is formed on the surface of an insulation film in advance, Cu is buried in the trenches and holes, and unnecessary Cu is removed by CMP (Chemical Mechanical Polishing) to form wiring.
In the damascene method, a plating method is mainly used to bury Cu. At present, to bury Cu by the plating method, various efforts are being made to bury a microstructure without involving a void (unfilled region). For example, an additive which gives priority in plating to the fine portions is contained in a plating solution so as to grow from the bottoms of the trenches and the holes (so-called bottom-up growth).
But, when a cross-section of Cu is observed, fine vacancies may exist in Cu even if Cu is thoroughly buried, and the Cu grain grows in a heat-treating step after the plating step, and the fine vacancies might aggregate to form voids. This phenomenon can be avoided by lowering the heat-treatment temperature or decreasing the heat-treatment time, but wiring reliability becomes lower because the grains do not grow sufficiently.
There is disclosed a technique that a bias sputtered copper-containing metal film containing different kinds of elements such as Ti, Zr and W is formed on a plated copper film (for example, Japanese Patent Laid-Open Application No. 2004-40022). Here, the content of the different kinds of elements to the bias sputtered copper-containing metal film is very small, and the different kinds of elements are used to spread into the plated copper film.